Costume Party
by the-misfortune-teller
Summary: At this point, Derek isn't sure why he ever trusts Stiles to behave himself properly in public. He's not going to complain all that much when he doesn't though. [established relationship/future fic/exhibitionism]


**Author's Note: **There's absolutely no excuse for this...I just wanted to write soemthing porny involving public sex and Stiles in a skirt! Sorry, not sorry! This sort of follows the time line from the epilogue to I'll Be With You Through The Dark, but isn't really part of that series. xx

* * *

"Why do you look so pleased?" Derek asks suspiciously when Stiles looks up from his phone.

"Scott says they're going to have a costume party instead of just a regular house warming party." Stiles grins, tapping out a reply, his attention drawn away from Derek again. "It'll be so awesome."

"No it won't."

::

"What's your general feeling towards matching costumes?" Stiles asks a few days later, sitting on the work top in Derek's kitchen in nothing but a pair of Green Lantern boxer briefs.

"Nothing but contempt." Derek huffs, batting Stiles' leg away when he tries to kick him. "I already told you, I'm not wearing a costume. Matching or otherwise."

"Aww, come on! I've got the most genius idea for a costume ever." Stiles pouts.

"Still no." Derek sets his coffee down by the sink and pads over to where Stiles is sat, putting his hands on the counter on either side of his hips and leaning forward to kiss him. Stiles begrudgingly returns the kiss before skating one hand across the front of Derek's sweat pants and rubbing at his cock through the thick fabric. Derek leans into his touch, resting his forehead against Stiles' chest and bites back a moan. "You're not going to make me change my mind this way you know."

"Not trying to." Stiles replies as he pushes down the waistband of Derek's sweats and pulls his cock free, curling his fingers loosely as he starts to jack him slowly.

Derek falls silent, breathing heavily as Stiles moves his hand faster and faster, until he comes with a grunt all over Stiles' stomach. Stiles leans back, a ridiculously smug smile on his face as he licks a drop of come off his thumb before dragging his fingers through the mess on his stomach, smearing it into his skin.

Derek pulls him into a kiss, trying to convey just how much he loves him with nothing more than his lips and tongue and a hand curled around the back of his neck.

::

"What are you wearing to this stupid party anyway?" Derek asks as he paces around his bedroom, holding his cell phone against his ear with his shoulder. He's planning on wearing his normal attire; dark jeans and a leather jacket but figures he'll throw on a white t-shirt instead of a gray one and if anyone queries his lack of costume, he can tell them he's come as Danny Zuko. After all, if he can't glare his betas into submission for questioning his choice of costume, he's failing as an alpha. He ignores the little voice in his head that helpfully points out that he frequently fails as an alpha in many other ways. He wants Stiles there with him; Stiles makes that little bit of his sub consciousness shut up.

"Not telling you." Stiles informs him, his voice echoing and tinny; he's got Derek on speaker again. "All I'll say is that Isaac is a better friend than both you and Scott. He isn't all morally opposed to costumes and fun and being a dork. We're costume buddies."

"You're both losers." Derek scoffs, flopping back on his bed and holding his phone properly. "Why can't you come over here and get ready?"

"I think you're seriously underestimating the lengths we're going to." Stiles replies. "Isaac's costume involves body paint and everything."

Derek growls softly in the back of his throat. He's not sure he likes the idea of Stiles and Isaac alone together while Stiles does whatever the hell he'll be doing to Isaac.

"Are you being jealous?" Stiles asks on the phone, the amusement in his voice evident. "Trust me, the painting Isaac thing? Very unsexy and he's definitely is not that way inclined."

"Why won't you tell me what you're wearing?" Derek tries again.

"Because I want to surprise you." Stiles tells him. "Look, I have a metric shit ton of stuff I need to do before tonight. I'll see you there, OK?"

"Fine."

"And no sulking in your bed because you think me and Isaac are getting up to some kind of painty sexy times."

Derek hangs up on him.

::

"Did Isaac tell you what they're coming as tonight?" Allison asks when she corners Derek in the kitchen, holding out a glass of punch. She's dressed as one of the little sisters from BioShock; if he didn't know that Allison is responsible for Scott's unreasonably high Gamerscore, he'd have been surprised.

"No. All I know is that there's body paint involved." He replies sniffing at the glass of punch he's been given; it's been spiked with the combination of herbs that Stiles found online, the combination that can get werewolves drunk.

"Isaac called me earlier asking where to buy pantyhose." Allison adds as she leans back against the counter and fiddles with the bow in her hair. "And Stiles turned up a few days ago asking for barrettes."

"Why does he want barrettes?" Derek asks with a frown. "He borrowed a pair of my boots for his costume." He has no idea what Stiles could possibly be wearing that involves barrettes and scuffed up boots.

Allison just shrugs, pushing away from the counter and wandering off to play hostess some more.

::

It doesn't take long to find out. Stiles and Isaac come barrelling into the backyard, both of them already drunk and raucous. He's still lurking in the kitchen, but hears Stiles loudly and repeatedly asking Erica where he is and sighs to himself, downing the last of his punch and heading out into the garden.

"Derek!" Stiles cries, wheeling around and abandoning Erica mid conversation to rush across the garden towards him.

"What in the hell are you supposed to be?" Derek asks, putting his hands on Stiles' shoulders and holding him at arm's length to take in his costume. Stiles is wearing a kilt that's short enough to be verging on illegal, shredded pantyhose and a ripped up white blouse that's straining across his shoulders. His normally pale skin is made paler by greasy face paint and there's huge, dark circles under his eyes. "Dead Britney Spears?"

"Zombie catholic school girl." Stiles grins hugely, gesturing to the worryingly realistic looking blood smeared over his chin. "I've been eating brains."

"Of course." Derek sighs, loosening his hold on Stiles and letting himself be dragged into a sloppy kiss. Stiles' mouth tastes like cheap rum and chocolate for some reason, and Derek keeps thinking that he probably shouldn't find the sight of Stiles in a skirt and pantyhose quite as appealing as he does.

::

Boyd tells him he looks like a pervert when he catches him watching Stiles. He maintains that it's not his fault, it's the way the blouse Stiles is wearing is too short, riding up all the time to reveal his stomach, the trail of dark hair that Derek is very much in love with. It's also not his fault that the skirt Stiles is wearing doesn't really fit him either and is hanging low enough to reveal the sharp jut of his hip bones to everyone.

"I'm allowed to look at him." He huffs over his plastic cup full of rum and coke. He's given up on Allison's punch because he doesn't really feel like getting drunk tonight. "We've been together for seven years. Looking at my boyfriend of seven years does not make me a pervert."

"It does when your boyfriend of seven years is dressed like a fifteen year old school girl." Boyd laughs. "Is Isaac doing it for you tonight as well?"

Derek contemplates letting the red seep into his eyes and growling at Boyd to shut up, but changes his mind when he remembers there are other people at the party, Allison's friends from work mostly, who would probably freak out if he tried to growl Boyd into submission. He doesn't really feel like getting yelled at for ruining Scott and Allison's party. Boyd flashes him a smug grin, clearly feeling as though he has won this round.

He settles for pushing Boyd roughly from his seat instead. Boyd looks less smug when he's sprawled on the floor, dark red punch soaking into the Punisher t-shirt he's wearing and claiming is a costume; Derek suspects that Boyd also didn't want to wear a costume but was bullied into it by Erica, who's strutting around somewhere dressed as Harley Quinn.

::

"I had to wear your boots." Stiles is explaining, gesturing wildly as he talks and spilling half of his drink. They're watching Scott and Isaac wrestling on the back lawn. Isaac's plaid skirt keeps riding up and Derek has never been more grateful to see a pair of black boxer shorts in his entire life. He wouldn't have put it past either Isaac or Stiles to be going commando under their skirts. Now he comes to think of it, he doesn't actually know what Stiles is wearing under his and rests his hand on Stiles' thigh, trying to casually slide it up and under his skirt.

"You're not even listening to me." Stiles grumbles, knocking the heel of his boot against Derek's shin and squirming in his lap.

"Yes I was."

"What was I talking about then?"

"Boots?" Derek tries, stilling his hand on Stiles' thigh, his fingers just under the hem of Stiles' skirt. Stiles, it turns out, isn't actually wearing pantyhose like Derek first thought. Oh no, Stiles is wearing _fucking stockings and a garter belt_, presumably because he wants to ruin Derek's life.

"Oh yeah." Stiles continues happily, as though Derek doesn't have his hand up his skirt, dragging his fingernails over his inner thigh. "We were going to fully commit and get women's shoes, but then Isaac reminded me that I fell over walking into the bathroom the other day and I figured heels might not be the best idea."

"You fell over tonight." Derek reminds him, his voice sounding thick to his own ears as he moves his hand a little further up. Stiles can't be wearing boxers, he tells himself as his fingertips continue to brush against bare skin, he'd have felt them by now. "When you forgot that there's three steps into their kitchen, not two."

"See, boots were clearly the best choice." Stiles tells him, finishing his beer and dropping the cup to the ground. He leans back against Derek's chest and sighs happily. "You know, if you want to find out if the whole 'men don't wear anything under their kilts' thing is true, you could just ask me."

"I prefer this way." Derek whispers, pressing a kiss against Stiles' neck. He's mostly got his attention focused on Stiles and the way his breathing is becoming shallower and more rapid, but he's also listening to make sure that none of the others are aware of what he's doing. He's eternally grateful that the lawn chair they're currently sitting in is beneath the large tree that dominates the garden and just outside the pools of light thrown out from the house.

"Yeah, well, I'm not exactly complaining." Stiles laughs, his pulse starting to race as Derek's fingers reach his hip. Derek frowns as his fingers brush against cool, smooth fabric, instead of...he's not sure instead of what, if he's honest.

"Are you wearing women's underwear?" He asks softly, his lips against Stiles' earlobe.

"Maybe." Stiles replies, shifting around in Derek's lap, grinding his ass back against Derek's semi erect cock. "Is that a problem?"

"Probably not." Derek manages to get out, moving his hand across to Stiles' crotch and tracing the outline of his cock through the thin material.

"I'm very, very committed to my costume."

"You're wearing my boots." Derek reminds him, enjoying the familiar feel of Stiles' dick fattening up beneath his fingers.

"I'm 95% committed to my costume."

Derek lets his head rest against the back of Stiles' shoulder and laugh shortly. "I like your level of commitment." He also likes the damp patch that's rapidly spreading across the front of Stiles' underwear.

"Could you, uh, give me a minute?" Stiles asks suddenly, wriggling up and off Derek's lap and turning to face him.

"No?" Derek replies in confusion, grabbing for Stiles' hips in a bid to pull him close again.

"Just trust me dude." Stiles grins, prising Derek's hands off his hips. "I'll be back in a few minutes. I'll make it worth your while."

Derek watches disappointedly as Stiles hurries away towards the house and gropes for the drink he'd been forced to abandoned earlier when Stiles had clambered into his lap complaining that he was bored and needed entertaining.

::

"Are they paying us any attention?" Stiles whispers as he sits back down on Derek's lap, making a little contented noise when Derek wraps his arms tightly around his waist.

"What?"

Stiles tilts his head to where Scott and Isaac are still play fighting on the lawn. Allison's sat with Boyd and Erica by the small bonfire they lit at some point during the night; he's not sure when. He's glad for once that the pack all seem to give him a free pass to go somewhere else and skulk whenever they get a fire going. The rest of the party guests have all gone home, and without checking his phone, Derek would guess it's probably getting close to 2am. No one's paying him and Stiles' the slightest bit of attention, too busy enjoying the buzz of alcohol, Allison's spiked punch and the crackling fire to look over to the dark patch under the tree.

"No. Not sure they even know we're over here."

"Well that's a little rude, but also kind of awesome." Stiles laughs as he twists around slightly so he can kiss Derek, sliding one hand up the side of his face and stroking his cheek as he licks into his mouth. When he finally pulls away, he gives Derek a wicked grin and reaches down between them to rub at Derek's dick through his jeans. "I've got a plan."

"I don't like your plans." Derek murmurs.

"Oh you'll like this one." Stiles smiles, nuzzling his nose against Derek's. "Trust me. Unzip your pants."

"What?"

"Don't ask questions, just do as you're told." Stiles laughs, Derek glances over his shoulder to see if anyone else heard what Stiles just said; there's nothing to suggest that they did so he nervously does as Stiles has asked. "No underwear?" Stiles adds, quirking an eyebrow.

"Shut up." Derek murmurs, his gaze flicking between Stiles and the others as Stiles reaches down again and pulls his cock free from his pants. Derek winces as the teeth of his zipper dig into his skin and taps Stiles on the leg until he lifts himself up slightly, allowing Derek to tug his jeans down a little further. "They're not stupid." He adds, glancing to the other end of the garden again. "They'll notice if you're suddenly sucking me off or something."

"Not going to blow you." Stiles murmurs, pulling something from the waist band of his skirt. "You're going to fuck me." He pops the cap off the bottle of lube he's holding and squirts a liberal amount onto his hand before reaching for Derek's cock again.

"Stiles, you'll hurt yourself." Derek hisses through clenched teeth as Stiles coats his cock with the lube. "And the pack are right there." He gestures to where the bonfire is still burning away, sending up sparks in to the dark night sky. "They'll hear us or see us. We can go back to my place if you want to screw around."

"I don't want you to fuck me in the loft." Stiles whispers, continuing to stroke Derek's cock. "I want you to fuck me here. Now."

Derek makes a whining noise, which Stiles hurriedly stifles with another kiss. "They'll definitely notice if I start, you know, fingering you." He's annoyed to feel himself blushing, worried that someone's going to notice their absence and come over to where they're sitting at any second.

"You don't need to." Stiles sighs, biting at Derek's bottom lip. "What do you think I was doing in the bathroom before?"

"Taking a leak?" Derek laughs shortly.

"Well I wasn't." Stiles replies, dragging his thumb over the head of Derek's cock. "Seriously? You really thought I was going for a piss?"

"You fingering yourself open wasn't exactly the first thing that sprang to mind."

"Look, this is all your fault for feeling me up before." Stiles murmurs, giving Derek's dick a squeeze and apparently judging it hard enough.

"I still think this is a bad idea." Derek sighs as Stiles turns around again, reaching behind himself to hitch up his skirt and pull his underwear to one side.

"Your dick says otherwise."

"Will you at least be quiet?" Derek asks, wrapping his hand around the base of his cock and lining up to push into Stiles, trying to go slow so he doesn't hurt him, very aware that Stiles is still slightly drunk and probably hasn't prepped himself as well as he likes to think he has. Stiles doesn't seem to be in the mood for slow and gentle right now though and pushes back roughly against him, gasping when Derek bottoms out. Derek has to bite down on his knuckles to stop himself from crying out; it's been a while since he topped and he thinks he might have forgotten how good it feels to be buried deep inside Stiles, his muscles clenching around his dick. He's very pleased to be getting his memory refreshed.

He hears Stiles make a whimpering noise and takes his hand out of his mouth, reaching around to cover Stiles' mouth instead, lest he attract the attention of the pack. He can't believe he's actually doing this; having sex with Stiles in full view of their friends, his pack. If they picked that moment to turn around, they'd see everything. Somehow, he doesn't think Scott will be too impressed if he catches him fucking Stiles in his backyard.

Not that he's doing much of the fucking right now; Stiles is rocking back against him, moving his hips almost imperceptibly, and whimpering quietly every time Derek's cock brushes against his prostate. He knows that normally Stiles would be lifting himself nearly off his cock, enjoying the feel of being spread open over and over again, but anything more than the way he's rocking his hips back and forth, those delicious, subtle movements, would draw too much attention and get them caught. The idea of Stiles having to restrain himself so much is incredibly hot and Derek shivers at the thought of it. He slips his free hand under Stiles' ridiculous skirt and starts stroking his cock through his underwear. Stiles sighs into the palm of his hand and leans back against Derek's chest, reaching up and digging his fingernails into his arm.

"This is possibly the stupidest thing we've ever done." Derek whispers into Stiles' ear, dragging his tongue up the side of his neck. "If they catch us..."

"Be quiet and they won't." Stiles murmurs into his hand, continuing to rock back and forwards on Derek's cock. The sheer absurdity of the situation, knowing that they could get caught at any second, the fact that Stiles is wearing a skirt and _fucking panties_, hell, the fact that it's been three days since they last had sex means that within minutes he's got his head bowed, forehead pressed hard against Stiles' shoulder as he feels his orgasm building low in his belly, little flashes of pleasure shooting up his spine.

He's so focused on the feeling of Stiles rocking slowly, torturously slowly, on his cock that he doesn't realise for a few minutes that Stiles has dragged his hand away from his mouth and is now just sucking on his first two fingers, licking and swirling his tongue around them. He forces himself to focus on Stiles for a minute, listening to his breathing and waiting for the telltale hitch that means he's about to come.

"I know what you're doing." Stiles mumbles around his fingers, his saliva trickling down the palm of Derek's hand. "You trying to hear if I'm close."

"Are you?" Derek breathes, continuing to stroke Stiles through the satin panties he's wearing. He likes the feel of the smooth fabric beneath his fingers, likes the way he can feel Stiles' pre-come soaking through the material.

"You tell me." Stiles moans, biting at Derek's fingers.

Derek rubs his lips against the side of Stiles' neck, feeling his pulse racing, his skin flushed and hot as he continues rocking back against Derek, his breath catching in his throat. All the little noises Stiles is making and the way his body is responding make Derek think he's close, but the way he's still moving so slowly is making Derek doubt himself.

But then suddenly Stiles is coming, spilling hot into the stupid satin panties and it's like a punch in the gut to Derek, the smell of Stiles all over his hand, the hungry noises he's making as he keeps sucking hard on Derek's fingers, the way his muscles clench around his cock and then he's coming too, wrenching his fingers free from Stiles' mouth so he can wrap his arm around his waist, to pull him down as close as possible. Stiles slumps forwards slightly, his hands on his knees and Derek is finally able to thrust up into him. He only manages a few thrusts before he's too wrecked to continue and flops back in the chair, pulling his hand out from under Stiles' skirt and wrapping both arms around his waist, dragging him back against his chest.

"Fucking love you." He pants in Stiles' ear, slipping his hand under Stiles' blouse and stroking the warm skin of his stomach.

"Love fucking you." Stiles counters with a laugh, turning his head to the side and nosing at Derek's temple. "Still think that was a bad idea?"

"Definitely not."

Stiles laughs again, lifting himself up slightly, pulling a face as Derek's softening cock slips out of him. He tugs the come soaked satin panties back into place and stands up, holding his hand out to Derek and pulling him to his feet.

::

They wander across the garden to where Allison, Erica and Boyd are sitting around the fire; Allison and Erica are talking quietly between themselves, Boyd's staring into the fire and taking long sips from a bottle of beer. He flashes Derek a knowing smile and mouths the word 'pervert' at him. Stiles is oblivious, flopping down on the ground beside Erica and leaning heavily against her legs.

"Ugh." She laughs, pushing his head away playfully. "You smell like you're gagging for it. Just take him home and fuck him, will you?"

Boyd's smile widens further as Derek shuffles uncomfortably. Stiles just laughs, stretching his legs out in front of him and leaning back on his hands as he forces his way into Erica and Allison's conversation.

::

Stiles does take Derek home so he can fuck him. Spends the best part of an hour opening him up with his tongue and fingers until Derek's nearly incoherent as he pleads with Stiles to 'just get on with it'; Derek feels like he's on the verge of tears, he's that desperate to feel Stiles inside of him. Stiles finally gets a tight hold on the back of his neck and pins him down against the mattress as he slowly pushes his dick inside of him, refusing to go faster no matter how much Derek begs him to.

Derek's orgasm is so intense that he thinks he may have blacked out for a second.

::

Scott turns up at the loft a week later and tells Derek that if he and Stiles ever have sex in his backyard again, he's going to call Stiles' dad and have them arrested for public indecency. He only knows because Boyd is not very good at keeping secrets. Especially if they're secrets that prove embarrassing and awkward for other pack members.

::

He refuses to let Stiles get rid of his costume. Just in case.


End file.
